Medicare Supplement Insurance, often called Medigap, is private health insurance designed to work alongside Original Medicare. It does not replace Medicare: Medicare Part A and Part B remain the foundation, paying their approved share of covered hospital and medical services first.
Your supplement policy then pays some or all of the remaining out-of-pocket costs, depending on the plan you choose. Those costs can include Part A hospital coinsurance, Part B coinsurance or copayments, blood, and, with certain policies, deductibles or emergency care during foreign travel.
That order matters. A Medigap policy is paired with Original Medicare, not with a Medicare Advantage plan. Medicare Advantage is an alternative way to receive Medicare benefits through a private insurer, usually with its own provider network, copays, and coverage rules.
You generally cannot use a supplement insurance policy to cover Medicare Advantage cost-sharing. Before enrolling, it is important to decide which path fits your preferred doctors, travel habits, budget, and comfort with unexpected medical bills.
Medigap plans are standardized in most states and identified by letters, so a Plan N policy covers the same core benefits regardless of which insurer sells it. Premiums, underwriting practices, customer service, and available household discounts can differ considerably, however.
Plan N, for example, may offer lower premiums than more comprehensive options in exchange for certain copays and no coverage for the Part B deductible or Part B excess charges. A local review can help clarify how those tradeoffs may look over time.
Your best opportunity to buy a supplement policy is typically during your six-month Medigap enrollment period, which begins when you are 65 or older and enrolled in Medicare Part B. During this window, insurers generally must sell you a policy without using medical underwriting to deny coverage or charge more because of pre-existing health conditions.
Outside that enrollment period, your options may be more limited unless you qualify for a guaranteed-issue right, such as losing certain other coverage. Prescription drugs are not included in Medigap, so many people who want drug coverage also enroll in a separate Medicare Part D plan. The practical goal is straightforward: keep Original Medicare’s broad access to providers while adding predictable protection against the expenses Medicare leaves behind.